This research will establish whether obsessive compulsive disorder (OCD) is familial. Given the inconsistencies and methodological limitations of prior research, we are proposing a blinded, controlled family study. Additional aims include: determining if other specific psychiatric disorders are more prevalent in first-degree relatives of OCD probands than those of controls; identifying demographic and clinical features which distinguish familial from sporadic (non-familial) cases of OCD; and conducting segregation analysis. OCD probands will be identified in four institutions in Baltimore and Washington, D.C. A control group, matched on age, sex, and race, will be identified in the residential neighborhood of each proband. All probands, controls, and their first-degree relatives will be directly and blindly examined using a standardized instrument to diagnose DSM-IIIR Axis I and Axis II psychiatric disorders. Final diagnoses will be made by consensus of two independent psychiatrists reviewing all case material, including medical records. Families with multiple affected members with OCD will be identified to possible future genetic linkage study.